Percussion or hammer drill

ABSTRACT

A percussion or hammer drill is provided including a drill plate arranged in the head end of a drill shaft, extending completely across the diameter of the drill shaft and comprising an open front face. Wedge-shaped cutting edges and flanks form two main cutters on the front face, whereby a plane running through the drill axis forms a mid-plane- of both main cutters. The main cutters form a tip angle in the range of approximately 140° to 180° and are separated by a central point.

This invention concerns a percussion drill or hammer drill.

During drilling, a percussion or hammer drill, also known as a masonry,concrete or stone drill, performs a percussive movement along thedrilling axis and a rotary movement about the drilling axis. Bothcomponents of its movement contribute to the removal of material in thedrill hole. The axial movement shatters the material in the drill hole.The rotary movement, by abrasion, causes a reduction of the materialinto drilling dust and carries the drilling dust away out of the drillhole.

Known percussion or hammer drills consist of a drill shaft with ahardened metal plate, the cutting plate, set in it. Spiral grooves runalong the shaft to evacuate the drilling dust from the drill hole. Thecutting plate extends across the diameter of the drill shaft. At itsexposed front surface, chip surfaces and free surfaces arranged in awedge shape form cutting edges. These consist of two linear main edgesoffset parallel to a plane in which the drilling axis lies, and atransverse edge linking the two main edges through the drilling axis. Inorder to achieve satisfactory centring when starting to drill, there isan angle not exceeding 130° between the two main cutting edges.

A task of this invention was to optimize removal of material in thedrill hole by suitable design of the cutting plate. This task isfulfilled by a percussion or hammer drill in accordance with claim 1 or15.

Such a percussion or hammer drill, also designated by the generic term“masonry drill”, consists of the standard layout of a drill shaft with acutting plate set in its head end. This cutting plate extends rightacross the diameter of the drill shaft and displays an exposed frontsurface. In this front surface—in a first embodiment—chip surfaces andfree surfaces arranged in a wedge shape form linear main cutting edgesdiametrically opposite to each other. In this arrangement, a planerunning through the drilling axis forms a central plane of both maincutting edges. With this arrangement of the main cutting edges, thepercussive energy is transmitted into the material more advantageouslythan with two main cutting edges offset parallel to a plane in which thedrilling axis lies. Thus the percussive energy is applied moreeffectively for demolishing material in the drill hole.

Further optimization of material removal in the drill hole is achievedby the fact that the two main cutting edges meet at an apex angle thatis greater than 130° and lies preferably in the region of 150° to 170°,for example 155° to 165°. The increase in apex angle similarly yieldsmore effective application of the percussive energy for removal ofmaterial in the drill hole.

In order to achieve satisfactory centring when starting to drill with awide apex angle, it is advantageous if a centring point is providedbetween the two diametrically opposite main cutting edges. The apexangle of this central point is then smaller than the apex angle betweenthe two main cutting edges. It may lie, for example, in the range of 80°to 130°.

Between the centring point and the chip surfaces or the free surfaces,as the case may be, it is advantageous to provide rounded transitionzones, in order to prevent stress concentrations between the centringpoint and the main cutting edges.

The centring point may be formed in plane symmetry with two planesperpendicular to each other, both of which pass through the drillingaxis and one of which also constitutes the central plane of the two maincutting edges. Such plane symmetry makes it possible to design acentring point that contributes to high material removal performance,high stability and outstanding resistance to wear of the cutting plate.As an alternative, the centring point can be designed with rotationalsymmetry.

According to another embodiment of the invention, removal of materialfrom the drill hole is optimized through corresponding shaping of thecutting plate. If the apex angle between the main cutting edges increaseradially from the inside towards the outside, the main cutting edges arebetter matched to the prevailing loads and removal of material isoptimized. The apex angle is then increased steadily in an outwarddirection along a main cutting edge by 20° to 40°. In this arrangement,the smallest apex angle then advantageously lies in the range between70° and 90°, and the greatest apex angle lies advantageously in therange between 90° and 130°.

In this connection it should be mentioned that in this embodiment, thetwo main cutting edges may, but need not, lie diametrically opposite toeach other.

Furthermore, the wear resistance of the cutting plate can be improved ifthe angle between the angle bisector of the cutting wedge and themid-plane of the two main cutting edges increases in an outwarddirection along the main cutting edges. In this respect, it has beenshown to be advantageous if this angle is increased from about 5° to25°.

The stability of the cutting plate is further enhanced by a cuttingwedge that is rounded off at the tip, the radius of this rounding beinggreater in the outer zone than in the inner zone.

In addition, it has proved advantageous, with the tip angles of 150° to170° used here, to increase the stability of the cutting edge by aprotective chamfer of the outer edge.

In what follows, an example of an embodiment of the invention will bedescribed with reference to the attached figures. These show thefollowing:

FIG. 1 A section of a percussion drill according to the invention in adrill hole;

FIG. 2 An elevation of a cutting plate;

FIG. 3 A top view of the front surface of the cutting plate shown inFIG. 2;

FIG. 4 A side view of the cutting plate shown in FIG. 2;

FIG. 5 A perspective view of the cutting plate shown in FIG. 2;

FIG. 6 An enlarged section of a perspective view of the cutting plateshown in FIG. 2;

FIG. 7 An elevation of a structural variant of the cutting plate shownin FIG. 1;

FIG. 8 A top view of the front surface of the cutting plate shown inFIG. 7;

FIG. 9 A side view of the front surface of the cutting plate shown inFIG. 7;

FIG. 10A perspective view of the cutting plate shown in FIG. 7.

The percussion or hammer drill 12 shown in FIG. 1 in a drill hole 10consists of a drill shaft 14 in the head end 16 of which is set a hardmetal plate 18, the drill plate or cutting plate as it is also known.This extends right across the diameter of the head end 16. Spiralgrooves 20, 20′ run along the drill shaft 14 to carry away the drillingdust out of the drill hole 10. The drilling axis is designated by thereference number 21. The percussion drill 12 performs a percussivemovement along the direction of the drilling axis 21 and a rotarymovement (see arrow 22) about the drilling axis 21. Both of thesecomponents of its motion contribute to the destruction of material inthe drill hole 10. The axial movement shatters the material in the drillhole 10. The rotary movement causes reduction of the material intodrilling dust by abrasion and carries away the drilling dust out of thedrill hole 10.

A first embodiment of a cutting plate 18 for a percussion or hammerdrill 12 according to the invention will be described with reference toFIGS. 2 to 6. Such a cutting plate 18 comprises a fixing shaft 24, toall intents and purposes prismatic in shape, which is welded into acorresponding slit in the head end 16 of the drill shaft 14 (see alsoFIG. 3, in which the outlines of the head end 16 are indicated by abroken line). The fixing shaft 24 is provided with narrow sides 26 and26′, each formed of a cylindrical face 28, 28′ and a flat face 30, 30′.The cylindrical face 28, 28′ in each case precedes the flat face 30, 30′in its direction of rotation and ensures that the drill 12 follows thedrill hole 10. The flat face 30, 30′ is set slightly back with respectto the diameter of the drill hole 10, thus reducing the friction of thenarrow sides 26 and 26′ in the drill hole.

The end of the cutting plate 18, which protrudes axially from the headend 16 of the drill shaft 14, displays a profiled front face 32, theprofile of which is described in greater detail below. In this exposedfront face 32, the chip surfaces 34, 34′ in combination with the freesurfaces 36, 36′ respectively are arranged together in a wedge shape soas to form the main cutting edges 38, 38′. As can be seen most clearlyin FIG. 3, the cutting plate 18 is provided with two linear main cuttingedges 38, 38′, arranged diametrically opposite to each other so that theplane 40 through the drilling axis 21 constitutes a central plane of thetwo main cutting edges 38, 38′. In the cutting plate 18 shown, thiscentral plane 40 forms an angle 44 of approximately 8° with the centralplane 42 of the fixing shaft 24. In this arrangement, the central plane42 intersects each of the two narrow sides 26, 26′ just behind thetransition point between the flat faces 30, 30′ and the cylindricalfaces 28, 28′.

FIG. 2 shows how the two main cutting edges 38, 38′ slope down from theinside towards the outside. In the central plane 40, they form what maybe termed an apex angle 46, of 162°, for example, in the cutting plate18 shown (in previous hammer drills this apex angle was no greater than130°). The effect of the very blunt apex angle 46, together with thecommon central plane 40 of the two main cutting edges 38, 38′, is thatthe percussive energy during drilling is strongly concentrated in thematerial being drilled, while friction is low. These two features thuscontribute to a significant optimization of shattering of the materialin the drill hole 10.

As can best be seen in FIGS. 2 and 5, the two main cutting edges 38, 38′are separated by a centring point 48 which is centred on the drillingaxis 21. This centring point 48 is in plane symmetry with respect to thetwo planes 40, 70, which are perpendicular to each other. The firstplane 40 is the central plane described in greater detail above. Thesecond plane 70 also includes the drilling axis 21 and is perpendicularto the central plane 40. As can be seen in FIG. 3, the centring point 48is oval in cross-section, the longer axis of the oval lying in thecentral plane 40 and the shorter axis in the plane 70. As can be seen inFIG. 5, the centring point 48 displays more or less the shape of acutter such as is commonly used in mining. However, it is significantlymore blunt in shape in the direction of the central plane 40. It shouldalso be noted that the centring point 48 contributes to higher boringperformance, greater stability and outstanding resistance to wear of thecutting plate 18. The rounded transition surfaces 52, 52′ are designedto prevent phenomena of stress concentration between the centring point48 and the main cutting edges 38, 38′, which could generate stress peaksleading to fracture during drilling. Another point to note is that thetransition surfaces 52, 52′ in the transition zones between the centringpoint and the chip surfaces can have a different radius of curvaturefrom those between the centring point and the free surfaces.

The cutting wedge constituted by the chip surface 34 and the freesurface 36 will now be described in greater detail with reference toFIG. 6. This cutting wedge will be defined, for each point on a maincutting edge 38, 38′, by a tangent 54 to the free surface 36 and atangent 56 to the free surface 36, in a sectional plane which isperpendicular to the central plane 40 and parallel to the axis ofrotation 21. As the projections of the chip surfaces 34, 34′ and thefree surfaces 36, 36′ in the cutting plate 18 of FIG. 6 in the sectionalplane are largely flat, the tangents 54, 56 effectively constitute thelines of intersection between the chip surface 34, 34′, resp. freesurface 36, 36′ and the sectional plane.

It should be noted that the point of the cutting wedge is rounded, or toput it another way, each of the main cutting edges 38, 38′ is roundedoff. A large edge radius here favours the stability of the cuttingplate. A smaller edge radius, on the other hand, favours drillingperformance. In the cutting plate 18, the edge radius of the maincutting edges 38, 38′, as can best be seen in FIG. 3, is fairly constantin the inner zone, but becomes significantly greater in proximity to thenarrow sides 26, 26′. By this means, the main cutting edges 38, 38′ arestrengthened in a particularly critical outer zone, but in the innerzone display a relatively small edge radius, which favours drillingperformance.

Returning to FIG. 6, it may also be noted that the angle of the cuttingwedge (referred to from now on as the wedge angle 57) along the maincutting edges 38, 38′ is not constant, but increases from the inside tothe outside. In the cutting plate 18 in FIG. 6, for example, the wedgeangle 57 shows a linear increase with the radius, from about 80° at thetwo transition surfaces 52, 52′ to about 110° at the two narrow sides26, 26′. It can also be observed that the orientation of the cuttingwedge along the main cutting edges 38, 38′ is not constant either. Thisorientation is measured as the angle 58 between the angle bisector 60 ofthe cutting wedge and the central plane 40. In the cutting plate 18 inFIG. 6, this angle 58 increases with the radius, from about 5° at thetwo transition surfaces 52, 52′ to about 25° at the two narrow sides 26,26′. Both the radially varying orientation of the cutting wedge and theradially varying wedge angle 57 of the cutting wedge give improvedstability to the cutting plate 18. This therefore becomes significantlystronger in its radially outer zone, that is to say where its tangentialvelocity is highest, and nevertheless displays outstanding drillingperformance. It should also be noted that a larger wedge angle 57 in theouter zone results in a larger amount of material, reducing wear on thecorners of the cutting plate, something that has to be kept in viewduring percussion or hammer drilling. Such wear on the corners leads,among other effects, to a reduction in the diameter of the drill hole10, so that slowing down wear on the corners extends the life of thedrill 12.

In addition, with the very blunt apex angle 46 used here, it has provedadvantageous to provide the outer edge of cutting edge, chip face andfree face with a protective chamfer 54, 54′ as a means of furtherincreasing the stability of the cutting plate. The shape illustrated forthe protective chamfer 54, 54′ is only one of a variety of possibleembodiments.

The cutting plate 18 in FIGS. 7 to 10 differs from the cutting plate 18shown in FIGS. 2 to 6 primarily in the design of the centring point 48.This no longer displays plane symmetry with two planes perpendicular toeach other, but displays rotational symmetry instead. In thisarrangement, the centring point 48 is given an apex angle 50 which issignificantly smaller than the apex angle 46 between the two maincutting edges 38, 38′, in order to enable satisfactory centring of thedrill when starting a hole. In the cutting plate 18 illustrated, theapex angle 50 shown as an example for the centring point 48 is 90°, thatis to say 72° less than the apex angle 46 of the two main cutting edges38, 38′. The centring point 48 of the cutting plate 18 is made to allintents and purposes rotationally symmetrical, with transition surfaces52, 52′ enabling a rounded transition towards the chip surfaces 34, 34′and the free surfaces 36, 36′. Key to references 10 Drill hole 12Percussion or hammer drill 14 Drill shaft 16 Head end 18 Hard metalplate 20, 20′ Spiral grooves 21 Drilling axis 22 Direction of rotation24 Fixing shaft 26, 26′ Two narrow sides 28, 28′ Cylindrical face 30,30′ Flat face 32 Front face 34, 34′ Chip surface 36, 36′ Free surface38, 38′ Main cutting edges 40 Central plane 42 Central plane 44 Angle 46Apex angle 48 Centring point 50 Apex angle 52, 52′ Transition surfaces54, 54′ Protective chamfer 57 Wedge angle 58 Angle 60 Angle bisector

1. Percussion or hammer drill comprising: a drill shaft with a head end;a cutting plate set in the head end and extending over a diameter of thedrill shaft and provided with an exposed front face; and chip and freesurfaces arranged in a wedge shape in the front face forming two maincutting edges positioned diametrically opposite to each other; wherein,both main cutting edges lie in a central plane passing through adrilling axis.
 2. Drill according to claim 1, further comprising an apexangle between the two main cutting edges in the range of approximately140° to 180°.
 3. Drill according to claim 1, further comprising an apexangle between the two main cutting edges in the range of approximately150° to 170°.
 4. Drill according to claim 1, further comprising an apexangle between the two main cutting edges in the range of approximately155° to 165°.
 5. Drill according to claim 1, further comprising acentring point, shaped between the two diametrically opposed maincutting edges, wherein an apex angle of the centring point is smallerthan an apex angle between the two main cutting edges.
 6. Drillaccording to claim 5, further comprising rounded transition surfacesprovided between the centring point and the chip surfaces and betweenthe centring point and the free surfaces.
 7. Drill according to claim 5,wherein the centring point is made rotationally symmetrical in shape. 8.Drill according to claim 5, wherein the centring point is shaped inplane symmetry with respect to two planes perpendicular to each other,wherein both planes run through the drilling axis and one of the twofurther constitutes the central plane of the two main cutting edges. 9.Drill according to claim 5, further comprising an apex angle of thecentring point in the range of approximately 80° to 130°.
 10. Drillaccording to claim 1, further comprising a wedge angle between the maincutting edges which increases radially in an outward direction. 11.Drill according to claim 10, wherein the wedge angle increases by 20° to40°.
 12. Drill according to claim 11, wherein the smallest wedge anglebetween the main cutting edges is in the range of approximately 70° to90°.
 13. Drill according to claim 1, wherein an angle between an anglebisector of the cutting wedge and the central plane of both main cuttingedges increases in an outward direction along the main cutting edges.14. Drill according to claim 1, further comprising a rounded maincutting wedge of greater radius in its outer part than in its innerpart.
 15. Percussion or hammer drill comprising: a drill shaft with ahead end; a cutting plate set in the head end which extends over adiameter of the drill shaft and is provided with an exposed front face;chip and free surfaces arranged in a wedge shape in the front faceforming two main cutting edges; and a wedge angle in the main cuttingedges which increases radially in an outward direction; wherein an anglebetween an angle bisector of the cutting wedge and the central plane ofthe two main cutting edges increases in an outward direction along themain cutting edges.
 16. Drill according to claim 15, wherein the wedgeangle increases by approximately 20° to 40°.
 17. Drill according toclaim 15, wherein the smallest wedge angle between the main cutting edgeis in the range between approximately 70° and 90°.
 18. (canceled) 19.Drill according to claim 15, further comprising a rounded main cuttingwedge with radius greater in its outer part than in its inner part. 20.Drill according to claim 15, wherein a plane running through a drillingaxis constitutes the central plane of the two main cutting edges. 21.Drill according to claim 15, further comprising an apex angle betweenthe two main cutting edges in the range of approximately 140° to 180°.22. Drill according to claim 15, further comprising an apex anglebetween the two main cutting edges in the range of approximately 150° to170°.
 23. Drill according to claim 15, further comprising an apex anglebetween the two main cutting edges in the range of approximately 155° to165°.
 24. Drill according to claim 15, further comprising a centringpoint provided between the two main cutting edges positioneddiametrically opposite each other, wherein an apex angle of the centringpoint is less than an apex angle between the two main cutting edges. 25.Drill according to claim 24, further comprising rounded transitionsurfaces provided between the centring point and the chip surfaces andbetween the centring point and the free surfaces.
 26. Drill according toclaim 24, wherein the centring point displays rotational symmetry. 27.Drill according to claim 24, wherein the centring point displays planesymmetry with respect to two planes perpendicular to each other, whereinboth planes run through a drilling axis and one of the two furtherconstitutes the central plane of the two main cutting edges.
 28. Drillaccording to claim 24, wherein the apex angle of the centring point isin the range of approximately 80° to 130°.